Improving wear behaviour of stainless steel AISI 321 by Plasma Nitriding and Diamond-like-carbon Coating

AISI 321 austenitic stainless steel, recognized for its exceptional corrosion resistance and thermal stability, is often limited by relatively poor wear performance in demanding engineering environments. This study proposes to systematically investigate the wear behaviour of plasma nitrided and duplex treated (plasma nitrided followed by diamond-like carbon coating) AISI 321 stainless steel. Plasma nitriding is expected to induce a hard, nitrogen-enriched expanded austenite (S-phase) layer at the surface, significantly enhancing surface hardness and wear resistance without sacrificing corrosion protection. Plasma nitriding provides the advantage of excellent nitriding potential control which can minimize the white layer formation. Further, it does not use ammonia and is an environmentally friendly process. The subsequent application of a diamond-like carbon (DLC) coating will further reduce friction and improve tribological performance due to its high hardness and low friction characteristics. It has been demonstrated that DLC coating adheres strongly to plasma nitride parts. IN the present study, wear tests, microstructural characterization, and surface property measurements will be conducted to compare the treated and untreated steels, aiming to elucidate the synergistic mechanisms responsible for improved durability. The outcomes of this investigation will contribute to the development of high-performance duplex surface treatments for austenitic stainless-steel applications where wear and corrosion resistance are paramount.

A review of the literature shows that most of the studies have been carried out on SS304 and SS316 alloy. Few studies exist on plasma nitriding of SS321 but no studies on duplex treatment. Hence, this study can develop novel surface engineering technology with potential applications.

The objectives of the work are as follows:

• To optimize the plasma nitriding pre-treatment by studying the effect of temperature on the microstructure and hardness of AISI 321.

• To deposit a uniform, adherent DLC coating on the optimized plasma-nitrided steel samples.

• To characterize the microstructure, phases, and surface morphology of the nitrided, and duplex-treated samples.

• To study the thermal stability of the nitrided layer and DLC coating at high temperatures, and its effect on wear properties.

• To evaluate the mechanical and tribological properties, specifically microhardness (Vickers Hardness test), adhesion (scratch test), and wear (room temperature and high temperature)

• To study the corrosion resistance of the plasma nitrided and duplex-treated AISI 321 steel.